In one embodiment, the invention is directed to a method for providing a protective coating on a metal-based substrate, comprising the following step:
(a) applying an aluminum-rich mixture to the substrate to form a discontinuous layer of aluminum-rich particles in a matrix of metallic bond coat alloy, wherein the amount of aluminum in the particles exceeds the amount of aluminum in the metallic bond coat alloy by about 0.1 atomic % to about 40 atomic %, and wherein the total amount of aluminum in the mixture is in the range of about 10 atomic % to about 50 atomic per cent.
In a second embodiment, the invention is directed to a method for providing a protective coating on a metal-based substrate, comprising the following steps:
(a) applying an aluminum-rich mixture to the substrate to form a discontinuous layer of aluminum-rich particles in a matrix of metallic bond coat alloy, wherein the amount of aluminum in the particles exceeds the amount of aluminum in the metallic bond coat alloy by about 0.1 atomic % to about 40 atomic %, and wherein the total amount of aluminum in the mixture is in the range of about 10 atomic % to about 50 atomic %; and then
(b) applying at least one coating layer over the discontinuous layer of aluminum-rich particles.
Aluminum diffuses from the aluminum-rich layer into the superalloy substrate, as discussed below. The discontinuous nature of the aluminum-rich layer prevents embrittlement.
In preferred embodiments, substantially all of the aluminum-rich material comprises non-oxide particles. Moreover, in many preferred embodiments, the aluminum rich layer is formed of two components. Component (I) usually comprises particles of aluminum and a second metal, such as nickel, while component (II) usually comprises particles of an alloy of the formula MCrAlY, where M is a metal like Fe, Ni, Co, or mixtures which comprise any of the foregoing. The aluminum-rich layer can be applied by plasma spray techniques, such as air plasma spray or vacuum plasma spray, or by high velocity oxygen fuel (HVOF).
In some embodiments, the layer formed with the aluminum-rich mixture is heat-treated after being applied, to allow diffusion of aluminum into the superalloy. Moreover, in certain embodiments, a conventional metallic bond layer is applied over the aluminum-rich layer, prior to deposition of a thermal barrier coating. The heat treatment mentioned above can alternatively be carried out after deposition of the thermal barrier coating.
Another aspect of this invention is directed to an article, comprising:
(i) a metal-based substrate; and
(ii) an aluminum-containing layer over the substrate, comprising a discontinuous layer of aluminum-rich particles. In many preferred embodiments, the article may also include a thermal barrier coating disposed over the aluminum-containing layer.
As mentioned previously, the aluminum-containing layer can be formed from a mixture of a component based on particles of aluminum and nickel, along with a component based on a conventional MCrAlY alloy. Moreover, a metallic bond layer can be disposed between the aluminum-containing layer and the thermal barrier coating.
Further details regarding the various aspects of this invention are provided in the remainder of the disclosure.